This invention relates to a substrate treating apparatus in which a certain treatment such as cleaning is conducted to front and rear surfaces of substrates such as semiconductor substrates and glass substrates for liquid crystals by immersing the substrates in a certain treating liquid.
In a process of manufacturing substrates such as semiconductor substrates and glass substrates for liquid crystals for use in precision electronic products, there has been known a conventional technology of a substrate treating apparatus wherein a substrate is immersed sequentially in a number of processing baths each filled with a certain type of treating liquid to conduct a surface treatment onto the front and rear surfaces of the substrate.
An example of such conventional apparatus is described below. The conventional substrate treating apparatus is provided with a liquid supply system. With use of such liquid supply system, a treating liquid is continuously supplied to a processing bath in which substrates to be treated are immersed in the treating liquid overflowing the processing bath. Thereby, any contaminants generated during the surface treatment or adhered on the surfaces of the substrates are discharged out of the processing bath together with the overflowing treating liquid. The thus discharged treating liquid is subjected to filtration with a filter or equivalent to remove the contaminants therefrom. Then, the treating liquid free of such contaminants is introduced to the processing bath again. In this way, the treating liquid is purified (refined) and circulated for repeated use after having been removed of the contaminants by the filtration.
Generally, in the above-mentioned apparatus using the liquid overflow method, the processing bath is equipped with a nozzle at a bottom portion thereof to supply a treating liquid. The treating liquid is supplied to the processing bath through the nozzle. However, merely providing the nozzle in the processing bath and causing the treating liquid to be supplied through the nozzle into the processing bath cannot supply the treating liquid in a stable manner, because the stream of treating liquid in the processing bath becomes disturbed with the supply of liquid. In other words, the surface treatment for the substrate becomes uneven (portion by portion) on the front and rear surfaces of the substrate due to an unstable stream of liquid, which may result in a failure of uniformity in the surface treatment on the substrate.
In order to eliminate the above drawback, generally, the processing bath is internally provided with a baffle plate in a plate form with a number of holes therein. The baffle plate is adapted for regulating the unstable stream of treating liquid supplied from the nozzle and allows the treating liquid to uniformly flow upward in the processing bath through the number of holes.
Generally, the baffle plate is composed of a resin material which is excellent in chemical resistance (resistance to corrosion). An example of such resin is polytetrafluoroethylene (PTFE). By using a baffle plate made of such a resin, the generation of contaminants resulting from erosion of the baffle plate caused by a chemical reaction with the treating liquid in the processing bath is prevented.
Due to the overflow of the treating liquid and other various factors, bubbles are likely to be introduced in the treating liquid which is being continuously supplied to the processing bath. Such bubbles are normally moved upward in a floated state by buoyancy and discharged in the air during the overflow of liquid. However, in the above constructed substrate treating apparatus provided with the baffle plate, some of the bubbles does not flow upward through the holes of the baffle plate due to the existence of the baffle plate and are adhered to an underside surface of the baffle plate. As the surface treatment is carried on, the adhered small bubbles are accumulated on the underside surface of the baffle plate. When the bubbles collect beyond a certain limit under the baffle plate, they abruptly depart from the underside surface of the baffle plate and move up in the treating liquid above the baffle plate through the holes during the surface treatment.
It should be noted that a non-negligible amount of contaminants which have been generated during the surface treatment are floating in the treating liquid. As the above mentioned bubbles proceed upward, these contaminants are also carried upward with bubbles. The contaminants carried by the bubbles proceeding upward are transferred onto a surface of the substrate and stay on the surface, and then oxygen contained in the bubbles is reacted with the substrate to generate contaminants which are likely to be adhered on the surface of the substrate. In this way, when bubbles, however small they may be in size, are trapped under the baffle plate and suddenly move upward through the holes of the baffle plate in a mass state, they adversely affect the surface treatment of the substrate beyond a permissible range.